Zeolites are very common materials in nature and there are many types of synthetic zeolites. It is estimated that there are about 100 types of synthetic zeolites and some of these are used in cracking catalysts. Examples of such cracking catalysts are those used in the well known fluid catalytic cracking (FCC) process and those used in the moving bed (TCC) process as described in U.S. Pat. No. 2,548,912. These types of catalyst contain crystalline zeolites, often referred to as molecular sieves, and are now used in almost 100% of the FCC and TCC type units, which process about 10 million barrels of oil per day.
Zeolites, or molecular sieves, have pores of uniform size, typically ranging from 3 to 10 angstroms, which are uniquely determined by the unit structure of the crystal. These pores will completely exclude molecules which are larger than the pore diameter. As formed in nature or synthesized, zeolites are crystalline, hydrated aluminosilicates of the Group I and Group II elements, in particular, sodium, potassium, magnesium, calcium, strontium, and barium, which can be exchanged with higher polyvalent ions, such as rare earths or with hydrogen. Structurally, the zeolites are "framework" aluminosilicates which are based on an infinitely extending three-dimensional network of AlO.sub.4 and SiO.sub.2 tetrahedra linked to each other by sharing all of the oxygens. The framework contains channels and interconnected voids which are occupied by the cation and water molecules. The cations are quite mobile and may be exchanged, to varying degrees, by other cations. Intercrystalline "zeolitic" water in many zeolites is removed continuously and reversibly. In many other zeolites, mineral and synthetic cation exchange or dehydration may produce structural changes in the framework.
As stated above, the uses for zeolites are many, but they typically must be combined with other materials when they are used in process applications. As an example, a synthesized zeolitic material, which is usually less than 4 microns in size, is combined with a binding agent, such as kaolin clay, silica sol, or amorphous silica, alumina, and zirconia as described in Demmel's U.S. Pat. No. 4,826,793 and then spray dried or extruded to produce a finished material that has the properties desired for the intended use. These properties may include attrition resistance, crush strength, particle size distribution, surface area, matrix area, activity and stability. Another method of producing a finished zeolite-containing product would be to produce the zeolite in-situ as described in Hayden's U.S. Pat. No. 3,647,718. While these patents deal mainly with FCC type catalyst, similar procedures are used in the production of zeolitic materials for TCC process applications. It is believed that in the manufacture of zeolitic moving bed and FCC type catalyst that some of the zeolite pores are blocked or buried within the matrix material and that the process described herein can remove this blockage and increase the available zeolite. So not only is the present process applicable to regenerated equilibrium catalyst, but it can also be used on the fresh zeolitic catalyst or additives before they are added to the FCC or TCC process for the first time.
An objective in refining crude petroleum oil has always been to produce maximum quantities of the highest value added products in order to improve the profitability of refining. Except for specialty products with limited markets, the highest value added products of oil refining with the largest market have been transportation fuels, such as gasoline, jet fuel and diesel fuels. Historically, a major problem in the refining of crude oil has been to maximize the production of transportation fuels. This requires a refining process or method which can economically convert the heavy residual oil, the crude oil fraction boiling above about 1000.degree. F., into the lighter boiling range transportation fuels. A major obstacle to the processing of this heavy residual oil has been the concentration of refining catalyst poisons, such as metals, nitrogen, sulfur, and asphaltenes (coke precursors), in this portion of the crude oil.
Since most of the oil refineries in the world use the well known fluid catalytic cracking (FCC) process as the major process for the upgrading of heavy gas oils to transportation fuels, it is only natural that the FCC process should be considered for use in the processing of heavy residual oils. Indeed, this has been the case for the last ten to fifteen years. However, the amount of residual oil that a refiner has been able to economically convert in the FCC process has been limited by the cost of replacement catalyst required as a result of catalyst deactivation which results from the metals in the feedstock. The buildup of other catalyst poisons on the catalyst, such as the coke precursors, nitrogen and sulfur, can be effectively controlled by using catalyst coolers to negate the effect of coke formation from the asphaltene compounds, using regenerator flue gas treating to negate the environmental effects of feed sulfur, and using a short contact time FCC process, such as that described in my U.S. Pat. No. 4,985,136, to negate the effects of feed nitrogen, and to some degree, the feed metals.
For the past twenty or more years the most widely used FCC catalysts have been zeolitic catalysts, which are finely divided particles formed of a matrix, usually silica-alumina, alumina or the like, having a highly active zeolitic material dispersed in the matrix. As is well-known, the zeolites used in such catalysts are crystalline and typically have a structure of interconnecting pores having a pore size selected to permit the ingress of the hydrocarbon molecules to be converted, and the zeolite has a very high cracking activity. Therefore, the highly active zeolite is dispersed in a matrix having a lesser cracking activity in a ratio providing the desired activity for commercial use. Typically used zeolites are of the faujasitic type, e.g., X-, Y- or L- type synthetic zeolites, and from about 5 wt. % to about 70 wt. % of the zeolite is employed. Such zeolitic FCC catalysts, their manufacture and their use in the FCC process are well known by those working in the art.
It is commonly accepted in the oil refining industry that vanadium contained in the residual oil FCC feedstock will irreversibly deactivate the zeolite by attacking the structure, and that this vanadium effect is more pronounced at temperatures above about 1330 F. It is also commonly accepted that catalyst deactivation by hydrothermal deactivation or by metals (e.g., sodium and vanadium) attack is irreversible.
In the operation of an FCC process unit (FCU) the process economics are highly dependent upon the replacement rate of the circulating catalyst (equilibrium catalyst) with fresh catalyst including additives, such as ZSM-5 and other zeolitic materials used for specific purposes in the FCU. Equilibrium catalyst is FCC or TCC catalyst which has been circulated in the FCU or TCC unit between the reactor and regenerator over a number of cycles. The amount of fresh catalyst addition required, or the catalyst replacement rate, is determined by the catalyst loss rate and that rate necessary to maintain the desired equilibrium catalyst activity and selectivity to produce the optimum yield structure. In the case of operations wherein a feedstock containing residual oil is employed, it is also necessary to add sufficient replacement catalyst to maintain the metals level on the circulating catalyst at a level below which the yield structure is still economically viable. In many cases, low metal equilibrium catalyst with good activity is added along with fresh catalyst to maintain the proper catalyst activity at the lowest cost.
In the processing applications that utilize zeolites, the material must be replaced as it looses its ability to perform the desired function. That is, the zeolitic material deactivates under the conditions employed in the process. In some cases, such as FCC and TCC type catalytic applications, fresh zeolitic material, in this case zeolitic catalyst or additives such as ZSM-5 (described in U.S. Pat. No. 3,703,886), are added on a daily basis. Fresh zeolitic catalyst is added daily at a typical rate of from 1% to as high as 10% of the process unit inventory to maintain the desired activity in the unit. Typically, as fresh catalyst is added to the FCC and TCC unit inventory, the operator to maintain the unit catalyst inventory within the design limits must withdraw equilibrium catalyst from the unit for disposal.
Copending application Ser. No. 08/581,836 of Robert E. Davis and David B. Bartholic discloses a process for improving the activity of zeolitic catalyst containing one or more contaminants which block the pores of the zeolite and adversely affect the activity of the catalyst.
In accordance with such Davis-Bartholic process, a slurry is formed of contaminated zeolitic cracking catalyst and as aqueous solution of a suitable acid, detergent and/or surfactant; the slurry is agitated to solubilize and/or dislodge contaminants which block the pores of the zeolite, and a portion of the solution containing the solubilized and/or solubilized contaminants is withdrawn from the agitated slurry in order to remove such contaminants and prevent them from being redistributed in the pores. The resulting treated catalyst having a reduced level of contaminants and improved activity is then separated from the remaining solution, washed, and recovered for use in a hydrocarbon processing unit.
Surprisingly, I have now determined that the activity of such a contaminated cracking catalyst can be significantly enhanced by a simpler and less expensive process, which is described hereinbelow.
It is believed that much of the deactivation mechanism for zeolitic materials results from zeolitic pore blockage, which can be reversed. This pore blockage can occur during the production stage by the retention of silica or other binding or matrix material in the zeolite pores. The pore blockage can also occur during the processing stage by silica that migrates to the pores, hydrocarbons from the feed or reaction products, or other materials present in the feed, or catalyst itself, that deposit or migrate into the zeolite pores, thereby blocking off access and reducing the activity of the zeolite. There are indications that hydrocarbon material may help to bind the silica and other feed and matrix material in the pores of the zeolite, or only hydrocarbon material may block the pore. This blockage prevents the reactants from entering the zeolite pores and therefore reduces the activity of the zeolite. Another cause of zeolite deactivation is the dehydration of the zeolitic structure.
Based on laboratory work, it is believed that there are various methods for reactivating these zeolitic materials based on (1) chemical treatments, which loosen or solubilize the materials blocking the zeolite pores, and (2) agitation, which aids in mechanically removing the pore blockage material. It is also believed that the dislodged or solubilized contaminant material removed from the pores must be separated from the reactivated product and that the most economical method to accomplish this reactivation in-situ, i.e., in conjunction with the process operations, as is described below.
As will be seen from the following discussion, it is believed that zeolitic FCC and TCC catalysts can benefit from the present invention, because, contrary to popular belief, the major cause of zeolitic catalyst activity decline is zeolite pore blockage which can occur, even during the catalyst manufacturing process, due to free silica or alumina, or compounds of silica or alumina, or other materials which are left behind and block the zeolite pore openings.
The primary objective of the present process is to integrate the reactivation of equilibrium FCC, and TCC, zeolitic catalyst with the unit operations so as to improve the economics. This process eliminates the cost of transporting the catalyst to an off-site location for reactivation and eliminates catalyst disposal costs. Also, by integration of the present reactivation process with the TCC and FCC operations, the costs and environmental problems associated with off-site reactivation will be greatly reduced. Another object of the present invention is to enable the removal of zeolitic catalyst deactivating materials without destroying the integrity of the catalyst and, at the same time, to significantly improve the activity and selectivity of the reactivated equilibrium FCC- and TCC-type zeolitic catalyst and additives. Another object of the present process is to reactivate zeolite-containing equilibrium catalyst using an environmentally safe and acceptable process.
Another object of the present invention is to improve the activity of fresh zeolitic catalyst and additives. Still another objective of the invention is to reduce the requirement for fresh catalyst replacement to an FCC unit, which will reduce fresh catalyst costs, transportation costs, equilibrium catalyst disposal costs, and unit catalyst losses. Other objects of the invention will become apparent from the following description and/or practice of the invention.